Cytochrome P450 (CYP) epoxygenases metabolize endogenous
polyunsaturated fatty acids to their corresponding
epoxides, generating bioactive
lipid mediators. The latter play an important role in vascular homeostasis, angiogenesis, and
inflammation. As little is known about the functional importance of extra-vascular sources of
lipid epoxides, we focused on determining whether
lipid epoxide-generating CYP
isoforms are expressed in human monocytes/macrophages.
Epoxides were generated by freshly isolated human monocytes and production increased markedly during differentiation to macrophages. Mass spectrometric analysis identified CYP2S1 as a novel macrophage CYP and CYP2S1-containing microsomes generated
epoxides of arachidonic, linoleic and
eicosapentaenoic acid. Macrophage CYP2S1 expression was increased by LPS and IFN-γ (classically activated), and
oxidized LDL but not
IL-4 and
IL-13 (alternatively activated), and was colocalised with CD68 in inflamed human tonsils but not in
breast cancer metastases.
Prostaglandin (PG) E(2) is an immune modulator factor that promotes phagocytosis and CYP2S1 can metabolize its immediate precursors
PGG(2) and
PGH(2) to 12(S)-hydroxyheptadeca-5Z,8E,10E-trienoic
acid (12-HHT). We found that CYP inhibition and
siRNA-mediated downregulation of CYP2S1 increased macrophage phagocytosis and that the latter effect correlated with decreased
12-HHT formation. Although no Cyp2s1
protein was detected in aortae from wild-type mice it was expressed in aortae and macrophage foam cells from
ApoE(-/-) mice. Consistent with these observations CYP2S1 was colocalised with the monocyte marker CD68 in human atherosclerotic lesions. Thus, CYP2S1 generates
12-HHT and is a novel regulator of macrophage function that is expressed in classical inflammatory macrophages, and can be found in murine and human
atherosclerotic plaques.